Luminescent rods are known in the art. WO2006/054203, for instance, describes a light emitting device comprising at least one LED which emits light in the wavelength range of >220 nm to <550 nm and at least one conversion structure placed towards the at least one LED without optical contact, which converts at least partly the light from the at least one LED to light in the wavelength range of >300 nm to ≤1000 nm, characterized in that the at least one conversion structure has a refractive index n of >1.5 and <3 and the ratio A:E is >2:1 and <50000:1, where A and E are defined as follows: the at least one conversion structure comprises at least one entrance surface, where light emitted by the at least one LED can enter the conversion structure and at least one exit surface, where light can exit the at least one conversion structure, each of the at least one entrance surfaces having an entrance surface area, the entrance surface area(s) being numbered A1 . . . An and each of the at least one exit surface(s) having an exit surface area, the exit surface area(s) being numbered E1 . . . En and the sum of each of the at least one entrance surface(s) area(s) A being A=A1+A2 . . . +An and the sum of each of the at least one exit surface(s) area(s) E being E=E1+E2 . . . +En.
WO2014/198619 describes a light emitting device comprising a light source adapted for, in operation, emitting light with a first spectral distribution, a first light guide comprising a first light input surface and a first light exit surface arranged opposite to one another, and further comprising an end surface extending perpendicular with respect to the first light input surface, and a second light guide comprising a second light input surface and a second light exit surface extending perpendicular with respect to one another. The first light guide is adapted for receiving the light with the first spectral distribution from the light source at the first light input surface, guiding the light with the first spectral distribution to the first light exit surface and to the end surface and coupling a part of the light with the first spectral distribution out of the first light exit surface into the second light guide and coupling another part of the light with the first spectral distribution out of the end surface. The second light guide is adapted for receiving light with the first spectral distribution coupled out of the first light guide at the second light input surface, guiding the light to the second light exit surface, converting at least a part of the light with the first spectral distribution to light with a second spectral distribution and coupling the light with the second spectral distribution out of the second light exit surface.
EP1795798 describes a light emitting device, comprising: an excitation light source that emits excitation light; a wavelength conversion member that absorbs the excitation light emitted from the excitation light source, converts its wavelength, and releases light of a predetermined wavelength band; a light guide in which the center part (core) of its cross section has a refractive index that is higher than the refractive index of the peripheral portion (cladding), and which guides the light emitted from the wavelength conversion member to the outside; and wherein the wavelength conversion member is produced by laminating a plurality of layers that wavelength-convert different wavelengths of light.
EP2947484 describes a light emitting device comprising at least one first light source adapted for, in operation, emitting first light with a first spectral distribution, at least one second light source adapted for, in operation, emitting second light with a second spectral distribution, a light guide comprising at least one first light input surface, at least one second light input surface and a first light exit surface, the at least one first light input surface and the first light exit surface extending at an angle different from zero with respect to each other, and a luminescent element arranged adjacent the first light exit surface, the light guide being adapted for converting at least a part of the first light with the first spectral distribution to third light with a third spectral distribution, guiding the second light and coupling at least a part of the third light and at least a part of the second light out of the first light exit surface, the luminescent element being adapted for converting at least a part of the second light to fourth light with a fourth spectral distribution.
WO2015/058979 describes a light emitting device comprising a first light source and a second light source adapted for, in operation, emitting light with a first spectral distribution and light with a second spectral distribution, respectively, a first light guide and a second light guide comprising a first light input surface and a first light exit surface, respectively, the light input surface and the light exit surface of the respective light guide extending at an angle different from zero with respect to each other, the first and second light guide being adapted for receiving the light with the first and second spectral distribution, respectively, at the first and second light input surface, converting at least a part of the received light to light with a third spectral distribution and light with a fourth spectral distribution, respectively, guiding the light to the first and second light exit surface, respectively, and coupling at least a part of the light with the third and fourth spectral distribution out of the first and second light exit surface, respectively, wherein the light having the first spectral distribution and the light having the second spectral distribution have different spectral distributions, and the light having the third spectral distribution and the light having the fourth spectral distribution have different spectral distributions.